A 60 year old man presented with a rapidly enlarging, painless mass in the left side of the anterior chest wall. He was otherwise healthy and had no previous medical or surgical history. Initial treatment by his general practitioner included a course of oral co-amoxiclav, which had no effect, and he was referred for further evaluation. Clinical examination showed a 10 cm round mass centred on/above the left fifth rib. It was non-tender and firm without evidence of inflammation. Blood tests showed a mildly increased erythrocyte sedimentation rate (11 and 40 mm/hour on two separate occasions) and white blood cell counts within normal limits (7.0–8.2 × 10
9 /litre on several occasions during the investigation). The initial radiological workup included
x ray of the thorax, which was normal, and ultrasound of the affected area, which showed generalised thickening of the pectoralis muscle and thickening of the costal cartilage, but no definite focal soft tissue abnormality, and a magnetic resonance imaging (MRI) scan was recommended. This showed swelling and oedema of the subcutaneous fat and anterior thoracic wall musculature, in addition to small pleural effusions (fig 1
). This was interpreted as probably being inflammatory in nature. For further evaluation, a surgical biopsy was carried out of the soft tissue. The biopsy showed skeletal muscle infiltrated by spindle cells scattered in abundant collagenous stroma with occasional lymphocytes (fig 2
). Focally, the muscle showed atrophic changes. No mitoses were identified and the spindle cells displayed bland nuclei similar to myofibroblasts. Immunohistochemically, the cells showed positivity for vimentin. Staining for cytokeratins (AE 1/3 and CAM 5.2 antibodies), S100 protein, HMB45, smooth muscle actin, smooth muscle specific actin, CD34, common leucocyte antigen, and desmin was negative. The suggested pathological differential diagnosis at this stage was of a non-neoplastic myofibroblastic process. However, in view of the clinical data further biopsies were suggested to ensure the lesion was fully sampled.
 | Figure 1 Initial magnetic resonance imaging scan of chest wall lesion showing subcutaneous and anterior thoracic wall oedema and bilateral pleural effusions. |
 | Figure 2 Light microscopic photograph (original magnification, ×200). Initial biopsy shows degenerating skeletal muscle with bland spindle cells scattered in abundant collagenous stroma. |
“The biopsy showed skeletal muscle infiltrated by spindle cells scattered in abundant collagenous stroma with occasional lymphocytes”
The lesion continued to enlarge rapidly over the next two months and a second MRI scan was carried out five weeks after the first (fig 3
). It showed a significant increase in involvement. The pattern was more mass like and was noted to extend into the anterior chest wall cavity, to abut the anterior pericardium, and there was a pericardial effusion in addition to bilateral pleural effusions.
 | Figure 3Second magnetic resonance imaging (MRI) scan of chest wall lesion taken six weeks after the initial MRI scan (fig 1). There was a noticeable increase in involvement, with the lesion more mass like and extending into the thoracic cavity, abutting the pericardium, (more ...) |
On the basis of the rapid growth it was decided to excise the lesion by a local resection including a segment of the anterior chest wall with parts of ribs two to four extending to the sternum. At surgery, the lesion was abutting but only superficially attached to the pericardium. The defect was reconstructed with a sandwich of Marlex mesh and methacrylate cement. A pectoralis flap was used and the skin was closed.
The surgical pathological specimen consisted of a 10 cm resection of part of the chest wall, including the chest wall lesion with three ribs and intercostal soft tissue. The parietal pleural surface was smooth and a cross section of the soft tissues showed a 4.5 × 4 × 3 cm ill defined process involving intercostal musculature. A cross section of one of the ribs revealed on gross inspection several areas of pus-like material, up to 0.5 cm in size, but no cortical bone destruction (fig 4
). On light microscopy, the soft tissue showed similar features to the original biopsy, namely an infiltrative spindle cell process with scantly scattered inflammatory cells and collagen deposition. Cross sections of bone were examined and, corresponding to the pale areas noted grossly, a dense mixed acute and chronic inflammatory infiltrate with abundant plasma cells was noted (figs 5,6
). In addition, there were foci of necrotic bone and pronounced osteoblastic activity around viable bone. A histological diagnosis of osteomyelitis with a striking myofibroblastic reaction was made. Special stains for microorganisms (periodic acid Schiff, Ziehl-Neelsen, Grocott, and Gram) were all negative and no material had been submitted for culture.
 | Figure 4 Cross section of a rib showing pale, pus-like material in one cross section. |
 | Figure 5 Light microscopic photograph (original magnification, ×200). Section through affected bone showing fibroinflammatory infiltrate with prominent osteoblastic rimming of bone. |
 | Figure 6 Light microscopic photograph (original magnification, ×400) showing inflammatory infiltrate from osteomyelitic focus. Note abundant plasma cells. |
After surgery the patient made a speedy recovery and was discharged after five days.
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